1. Field of the Invention
The present invention relates to a radiation system, a lithographic apparatus, a device manufacturing method, and a device manufactured thereby.
2. Description of the Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. Lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that circumstance, a patterning device, such as a mask, may be used to generate a circuit pattern corresponding to an individual layer of the IC, and this pattern can be imaged onto a target portion (e.g. including part of one or several dies) on a substrate (e.g. a silicon wafer) that has a layer of radiation-sensitive material (resist). In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam of radiation in a given direction (the “scanning” direction) while synchronously scanning the substrate parallel or anti-parallel to this direction.
A lithographic apparatus as described above usually includes an illumination system and a radiation source. The radiation source provides the required radiation for irradiating the patterning device.
A problem in presently available EUV illumination systems is that non-linear effects occur when a high power EUV radiation beam is generated. These known illumination systems employ a radiation source with a laser produced plasma (LPP) or discharge produced plasma (DPP). Several problems are associated with radiation sources with a laser produced plasma when high power is involved: nozzle degradation, nozzle material sputtering, nozzle thermal load, gas recycling, vacuum system gas load, low repetition rate, low conversion efficiency, inhomogeneous emission profiles, etc. Current problems with discharge produced plasma at higher powers are: extended source size, elongated shape of the radiation source, pinch size depending on all system parameters, low conversion efficiency, etc.